Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2000-07-18
2002-06-18
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S043000, C127S046200, C127S048000, C127S052000, C127S054000
Reexamination Certificate
active
06406548
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for obtaining sucrose from sugar cane.
The production of cane sugar for human consumption generally comprises two distinct operations, namely the production of raw sugar and the production of refined sugar. Production of raw sugar typically takes place at a sugar mill. In the mill, sugar cane stalks are chopped into pieces and the pieces are crushed in a series of mills in order to extract the juice. The juice from the first set of roller mills is referred to as “first juice,” while the total juice from all the roller mills in the process is referred to as “mixed juice.” The juice is normally limed, deaerated and clarified (i.e., removal of suspended solids, usually by sedimentation). The clarified stream is referred to as “clarified juice.” The juice is then evaporated to a thick syrup (known as “evaporated juice” or “thick juice”), and crystallized in a vacuum pan. The “massecuite” (i.e., mixture of sugar syrup and crystals) produced in the vacuum pan is stirred in a crystallizer, and the mother syrup is spun off from the raw sugar crystals in a centrifugal separator. The solid sugar in the centrifugal basket is washed with water to remove remaining syrup. The solid crystalline product is termed “raw sugar.” The syrup remaining after multiple stages of crystallization and centrifugation is referred to as “cane mill molasses” and is typically used for animal feed or fermentation syrups.
Raw sugar from the mill is usually transported to a sugar refinery for further processing. In a conventional cane sugar refining process, the raw sugar is first washed and centrifuged to remove adherent syrup, and the “affined sugar” thus produced is dissolved in water as “melter liquor.” The syrup removed from the surface of the raw sugar is known as “affination syrup” and is broadly similar in composition to the mother syrup from the raw sugar crystallization. The affination syrup is processed in a “recovery section” through a series of vacuum pans, crystallizers and centrifugal separators similar to those used for the production of raw sugar, to recover an impure crystalline sugar product which has approximately the same composition as raw sugar. This recovered sugar product is dissolved in water, along with the affined raw sugar, to make melter liquor. The syrup remaining after the multiple stages of crystallization and centrifugation is referred to as “cane refinery molasses,” and is typically used for animal feed or fermentation syrups.
The melter liquor is purified, generally by the successive steps of clarification and decolorization, and the resulting “fine liquor” is crystallized to give refined sugar (also known as “white sugar”). The clarification step usually involves forming an inorganic precipitate in the liquor, and removing the precipitate and along with it insoluble and colloidal impurities which were present in the melter liquor. In one of the clarification processes commonly used for melter liquor, termed “carbonatation” or “carbonation,” the inorganic precipitate is calcium carbonate, normally formed by the addition of lime and carbon dioxide to the liquor. The calcium carbonate precipitate is usually removed from the liquor by filtration. Another clarification process, termed phosphatation, involves adding lime and phosphoric acid to the liquor, producing calcium phosphate precipitate.
The molasses produced in cane mills and refineries contains a substantial concentration of sucrose (e.g., 35-55% by weight on a dry solids basis). However, that sucrose cannot be recovered readily by additional crystallizations, because the molasses contains such a high concentration of impurities, including invert sugars (a mixture of glucose and fructose). The sucrose in the molasses could be sold for a far higher price than the molasses, if only the sucrose could be separated from the other constituents of the molasses in an economical way. However, the prior art has failed to provide a practical and cost-effective way to make this separation for cane syrups where invert is a significant component.
Chromatographic separation is used to desugar beet molasses and has been proposed for cane, but beet molasses has no invert and it is more straightforward to separate the sucrose. Chromatographic separation is an expensive process for cane.
Conventional dead end filtration is incapable of separating sucrose from macromolecular impurities in cane juice. Several methods of using microfiltration and ultrafiltration for purification of juice with reduced lime use have been reported, but these methods generally involve inserting microfiltration or ultrafiltration membranes into the conventional can process at one or more points.
There is a long-standing need for improved processes for obtaining sugar from cane that avoid or at least minimize one or more of the problems existing in the previously used processes.
SUMMARY OF THE INVENTION
The present invention relates to a process for producing sugar from cane. A sucrose-containing feed juice that has been obtained from sugar cane is filtered through a first ultrafiltration membrane that has a first molecular weight cutoff. This ultrafiltration step produces a first ultrafiltration permeate and a first ultrafiltration retentate. The first ultrafiltration permeate is filtered through a second ultrafiltration membrane that has a second molecular weight cutoff that is lower than the first molecular weight cutoff. This second ultrafiltration step produces a second ultrafiltration permeate and a second ultrafiltration retentate. The second ultrafiltration permeate is nanofiltered through a nanofiltration membrane, thereby producing a nanofiltration permeate and a nanofiltration retentate. The nanofiltration retentate has a higher concentration of sucrose on a dry solids basis than the feed juice introduced into the first ultrafiltration step, and can be used in evaporation and crystallization operations to produce crystals of white sugar.
In one embodiment of the invention, the sucrose-containing feed juice is manufactured by macerating sugar cane or pieces thereof, thereby producing a macerated material that comprises pulp and liquid, and then separating the liquid in the macerated material from the pulp, for example by one or more of centrifugation, conventional filtration, or screening. In one particular embodiment, the cane is macerated by first passing it through a hammer mill, and optionally it can subsequently be passed through a grinder, whereby the cane is converted into a mixture of pulp and sucrose-containing liquid. Preferably, no more than about 5% by weight of the sucrose present in the cane remains in the pulp after the liquid is separated therefrom, more preferably no more than about 3%.
After separation of the fibrous pulp from the liquid, and before the first ultrafiltration, the process can optionally include an additional step or steps to remove residual beet cane and silt from the separated liquid (juice). This can be done by screening and/or filtration. Preferably the screening or filtration removes at least 90% by weight of all fibers and silt having a largest dimension of about 150 &mgr;m or greater, more preferably at least 90% by weight of all fibers and silt having a largest dimension of about 50 &mgr;m or greater.
It is preferred to adjust the pH of the feed juice to about 6-8, for example by the addition of a base, prior to ultrafiltration. This can help minimize formation of invert.
The first ultrafiltration membrane preferably has a molecular weight cutoff between 2,000 daltons and a pore size no greater than about 0.2 microns. More preferably, it has a molecular eight cutoff of about 4,000-200,000 daltons. The first ultrafiltration permeate preferably has a color of about 3,000-15,000 icu. (All color values given herein are determined on an ICUMSA scale.)
The process of the present invention can be operated at a number of different process conditions. As representative examples of such conditions, the feed juice can be at a temperature of about 140-200°
Donovan Michael
Hlavacek Marc
Jansen Robert P.
Reisig Richard C.
Walker Gordon
Brunsman David
Tate & Lyle Industries, Limited
Williams Morgan & Amerson P.C.
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